



assesses 3 either of the electron discharge or barrier-layer type is poled so that negative pulses only pass. The rectiiier output is connected through blocking condenser 2| and grounded resistor 22 to K2 oi' the second stage.

Initially, when a stese is energized. it may assume any one of three positions, to be described in detail later. Inasmuch as successive trigger pulses cause a stage to go through a sequence of three positions. it is immaterial which position assumed by a stage. In practice, a stage will be set in the desired initial position by means of an auxiliary switch to connect the two cathodes directly together or by trigger or both. convenience. let it be assumed that stage the condition where tube Tl is cut on.' and tube T2 is conducting heavily. In that condition. the potential of cathode K2 will be at its x2. Thus the potential of KI will be above groimd but lower than the potential of cathode K2.

Now assume that a negative trigger pulse appears at K2. lhe potential of K2 drops sharply (a drop will be referred to when the potential becomes more negative and a rise will be referred to when the potential becomes more positive with respect to ground) When the potential of cathode K2 drops. the potential of grid G2 tends to follow the cathode potential downwardly by virtue of the diode action between these two electrodes. Then when the potential of grid G2 drops. the potentials across condensers 22 and 2l becomes dliferent. It will be remembered that while tube T2 was conducting heavily, prior to the trigger pulse, the potential of grid G2 and cathode K2 were substantially equal and both were well above ground. Thus a certain dinerdrops sharply and follows the potential of cathode K2. condenser 2| will discharge. Condenser 2l on the other hand, will charge additionally.

By virtue of condensers 2i and 22, the potential of grid G2 will remain negative after the puise has passed and the potential of K2 Accordingly. tube T2 will begin to cutpotential of anode A2 will start to rise. same time, the positive rise in potential A2willbetransmittedtogridGl and swing this grid positive. 'I'he potenanode Ai begins to drop and. through the coupling to G2. the well-known multi-vi- In um am swing when 'n is ut-on and 'rl cross connections between of grid G2 has assumed a certain value ground. this depending upon the of resistors 22 and 2|. This po- G2 is low enough so that the potential of cathode K2 will be above that of gridG2.thusassuringcut-oi2ofT2. Thepotential of grid G2 remains constant long enough so that grid G2 becomes less negative with respect to cathode K2 for the duration of the pulse and tube T2 begins to conduct. The potential at anode A2 starts to drop and tube TI begins to cut-olf. Thus the potential of cathode KI also begins to drop. When the potentials oi' cathode Kl and K2 equal each other, rectiers XI and X2 cease to conduct and the cathodes are effectively disconnected. When the cathodes of TI and T2 are disconnected, the cathode resistors. which are high in value, cause degeneration. particularly in tube T2. In this tube, no condenser shunts the cathode resistors. At this time, the see-saw action tending to cut in tube TI and cut-off T2 ceases and both tubes are stabilized at a condition of intermediate conduction where both tubes conduct some current.

The reason that the ilrst trigger pulse (when TI was cut-oi!) caused both tubes to go through a complete change, and did not stop at an intermediate position, will now be explained. When tube T2 conducts, condenser 2i has a difference oi' potential impressed across it which is a function of the division of potentials between resistor 22 and the parallel combination of 2li and R2 and R22. 'I'he quick discharge of condenser 2l through grid G2 and cathode K2 drops the potential of grid G2 sharply. When the pulse is over, the potential of cathode K2 begins to rise quickly while G2 remains negative. Due to the presence of condensers 2l and 2i, G2 remains negative long enough for the action of TI to cut-oi! T2 completely. Hence T2 cuts oi! completely. When the succeeding trigger pulse reaches K2 with T2 cut-oil'. condenser 2| cannot discharge. at least to any substantial extent through tube T2. Hence tube T2 begins to conduct a little due to the negative pulse. The reaction on tube Ti is as expected in a simple multivibrator up to a certain point. When the potentials oi' cathodes Kl and K2 are equal the lack of coupling between Kl and K2 causes TI and T2 to stop reacting upon each other and both tubes conduct slightly. If the trigger pulse duration is excessive. then of course the intermediate tube condition will not be a point of equilibrium.

'Ihe pulse duration for triggering to intermediate condition must be shorter than the time constant of the circuit of condenser 2| when tube T2 is cut-oil. On the other hand, when T2 conducts heavily, the time constant of the G2 circuit must be shorter than the pulse duration. 'I'his is possible because of the diode action between G2 and K2.

At this stabilized intermediate position, the potentials at anodes Al and A2 are about equal. A succeeding negative pulse at cathode K2 momentarily destroys the condition of intermediate equilibrium and permits tube T2 to conduct more heavily and tube Ti to cut-ott. 'I'his additional pulse cannot cause tube T2 to cut-oi! and tube Ti to conduct heavily. In other words, this additional negative trigger Pulse cannot cause the stage to step back into the second state or condition where tube T2 is cut-od completely and tube TI conducts heavily. This is due to the fact that no grid current in T2 can flow to discharge ctgrixdzenser 2l while G2 is negative with respect In the intermediate condition where Ti and T2 both conduct slightly. G2 is sugnuy negative m K2, but above cut-otr. Hence a negative pulse on K2 tends to make T2 conduct more heavily.

7 sumedthatstrasoapacitancesaremoreorleu similar as regards the two tube circuits oi a stage. andonthisassumptimthevaluesotcondensers it and 2t should be within about 5% of each other.

ors and the valu ot the cathode resistors will depend upon the amount of tube current to be passed at full tube conduction. In general, the value of a cathode resistor, that is the sum o! Ri andRil rorexample.wil1begovernedbythe same consideration as obtain in a conventional counter circuit. The location o! the point for connectingtherectiilerisnot criticalandwillbe determined by the cut-oil' characteristics oi the vacuum tube used, the characteristics oi the rectifier and the desired characteristics oi.' the circuit as a whole, particularly the intermediate current condition. The two cathode circuits, however, should be as much alike as possible within about 5%. Condemer t, across the cathode resistors in TI. is provided ior the purpose oi' sharpening the pulse in the anode circuit of this tube. This condenser may have a value oi about 300 mini. although this value may vary. I! desired. this condenser may be omitted.

lhe rectiiler may consist either oi a diode or any other electron discharge device or may be ot the crystal type. such as germanium. This lattertypeotrectierhasahighratiooiback to forward resistance and is well suited for this type oi circuit. A selenium rectifier is also satisfactory.

The trigger puise-is preierably sharp and has a duration suitable 1er operating a stage. As a rule, the trigger pulse requirements will be largely determined by the necessity for reaching and stopping at the intermediate condition. I! the pulse is too long or too great in amplitude, there may be instability. However, the circuit, as described, will operate quite satisfactorily over a substantial variation ot pulse amplitude and duration irom the pulse for which the stage is designed. As is understood. a stage may be designed to accommodate pulses oi diii'erent duration and amplitude. Precision requirements come into being when high speed operation ot a stage is desired.

The trigger iniection point has been described as at K2. Trigger pulses ol' suitable positive amplitude may be applied to G2 or oi' suitable negative amplitude to A2.

Ingeneralitisprei'erredtoapplythepuisto the cathode of tube TI as distinguished from the cathode of TI. However, the pulse input may be applied to the system generally under the same conditions as is true in a convtional multivibrator.

What is claimed is:

l. A circuit having three conditions oi stable equilibrium, said circuit comprising two vacuum tube ampliilers. each ampliner having a cathode. control grid and anode, cross connections between the anodes and control grids, each such cross connection including a resistor, each oi said tubes havingaresistorbetween groundandits control grid. resistors between the cathodes of said tubes and ground, each cathode having separate resistors. rectiilers cross-connected between the cathodes and intermediate cathode resistor points and poled so that the direction of conduction is from an intermediate resistor point toacathode.loedresistorsinsaidanodecir cuit. said circuit when energized having one stableposldonwithonetubeconductingheavilyand d The location ci point Pi on the cathode resisttheothertubecutoiioranotherstablepositicn vice versa, or still another stable position with both tubes conducting slightly.

2.Acircuithavlngthreeconditionsoistable equilibrium. said circuit comprising two vacuum tube amplifiers, each ampliner having a cathode. control grid and anode, cross connections between the anodes and control grids. each such cro connection including a condenser and resistor in shunt, each of said tubes having a resistor between ground and its control grid, resisters between the cathodes oi said tubes and ground. each cathode having separate resistors. rectiilers cross-connected between the cathodes and intermediate cathode resistor points and poled so that the direction ot conduction is from an intermediate resistor point to a cathode. and load resistors in said anode circuit.

3. A circuit having three conditions oi stable equilibrium. said circuit comprising two vacuum tube ampliilers. each ampliiler having a cathode, control grid and anode, cross connections between the anodes and control grids. each such cross connection including resistor and condenser in shunt therewith. one oi said tubes having a condenser and resistor in shunt therewith between ground and its control grid. resistors between the cathodes oi said tubes and ground, each cathode having separate resistors. rectiiiers cross connected between the cathodes and intermediate cathode resistor points and poled so that the direction oi' conduction is from an intermediate resistor point to a cathode, load resistors in said anode circuit. and a puise intake circuit for said one tube, said pulse intake requiring pulses oi' a polarity tending toward space current through said one tube. said circuit being adapted to have one tube conducting heavily and the other tube cut oil'. or vice versa, or to have both tubes conducting slightly when said one tube is successively pulsed. the tubes, grid to anode cross connections. grid and cathode resistors being symmetrical, the condensers and resistors for the grid circuit oi said one tube having such values that the time constant for such grid circuit when said one tube is cut oil, is greater than the pulse duration.

4. A circuit having three conditions of stable equilibrium, said circuit comprising two vacuum tube ampliiiers. each ampliiler having a cathode, control grid and anode, cross connections between the anodes and control grids. each such cross connection including a resistor and condenser in shunt therewith, said two tubes each having a resistor between ground and the control grid, a condenser in shunt to the grid resistor for only one oi' said tubes. resistors between the cathodes of said tubes and ground, each cathode having separate resistors, rectiiiers cross connected between the cathodes and intermediate cathode resistor points and poled so that the direction ot conduction is from an lntermediate resistor point to a cathode, load resisters in said anode circuit. and a pulse intake circuit for said one tube only, said pulse intake requiringpulsesotapolaritytendingtocause conduction through said one tube. the tubes. cross connections, grid and cathode resistors being symmetrical as for a multi-vibrator, the grid to ground resistor and condenser i'or said one tube having a time constant longer than a pulse duration and oi the order oi about onehalioithetimeconstantoithegridtoanode cross circuit. said circuit being adapted to have one habe conducting heavily and the other tube 

